He looks pretty good for a mentally diseased, substance-abusing strangler.

Preppy killer Robert Chambers was back in a Manhattan court on his cocaine sale case yesterday. Clean-shaven, beefier, alert and far less pale, he was the healthiest he’s looked since cops busted into his alleged East 57th Street drug den in October.

The new and improved Chambers appeared in public just as his lawyer filed new papers elaborating on his psychiatric defense – namely, that his addictions to cocaine and heroin rendered him unable to intentionally sell a pound and a half of coke to undercover cops.